1. Field of the Invention
The present invention relates to a servo control apparatus, a servo control method, and an information reproducing apparatus, and more particularly relates to a servo control apparatus for and a servo control method of carrying out a servo control when information is optically reproduced from an information record medium, such as an optical disc, etc., and an information reproducing apparatus having the same.
2. Description of the Related Art
In recent years, a so-called DVD having a record capacity increased by several times that of a conventional CD (Compact Disc) has been widely generalized as an information record medium on which image and audio information whose amount corresponds to that in one movie can be recorded.
Recently, in addition to the specifications for a read-only DVD currently getting generalized, specifications for a so-called DVD-RW (hereafter, the specifications are merely. referred to as DVD-RW specifications) are being established as specifications for. a DVD that allows recording and reproducing of the information a plurality of times, and reproducing of the information even if it is used in an information reproducing apparatus for the read-only DVD.
In the DVD-RW specifications currently being established, a groove track meandering at a constant frequency is formed on the DVD-RW as an information track where the information is optically recorded and reproduced.
The groove track is meandered to generate a reference recording clock signal having an accurate frequency synchronized with a rotation of the DVD-RW by detecting the frequency of meandering at the time of recording the information on the DVD-RW.
The DVD-RW basically has a recording capacity substantially equal to that of the read-only DVD. Thus, unauthorized duplication of the image information, etc. recorded in the read-only DVD can be done.
However, the image information, etc. recorded in the read-only DVD is usually protected by the Copyright Act. Thus, the rampancy of the unauthorized duplication as mentioned above is extremely disadvantage for the owner of the copyright.
Therefore, as a countermeasure against the unauthorized duplication, the DVD-RW specifications specifies that an area on the DVD-RW corresponding to an area in which a control information for reproduction control is recorded in the read-only DVD, is defined as a non-recordable area (hereafter, referred to an embossed area).
Incidentally, in the information reproducing apparatus for an actual DVD-RW, it is desirable that information recorded on an optical disc expect the DVD-RW, namely, CD, the read-only DVD, a DVD-R (DVD-Recordable) on which an information can be recorded only one time, etc., can be also reproduced by the information reproducing apparatus.
In the case when the information recorded on the various optical discs is respectively reproduced in the above-mentioned information reproducing apparatus having a so-called high compatibility, it is required that servo control, such as a so-called tracking servo control, focus servo control, etc. is performed. Thus, when the reproduction is started, it is necessary to carry out start processing for starting the servo control, and then set a servo loop at a closed state.
At this time, the start processing needs to use a detection signal from each optical disc, such as a reproduction RF signal, etc. However, if one information reproducing apparatus reproduces the information from the various optical discs as the above-mentioned case, it is necessary to carry out the start processing by first radiating a light beam to a position on the optical disc (hereafter, merely referred to a common detection position) at which the detection signal is obtained in all kinds of optical discs.
Here, according to the specifications of each optical disc, an outer position 25 mm away from a center of each optical disc corresponds to the above-mentioned common detection position.
Therefore, the information reproducing apparatus having the above-mentioned compatibility first emits a light beam to an outer position 25 mm away from a center of an loaded optical disc, and thereby obtaining a detection signal, and then carries out the start processing by using it.
Then, the reproduction of the information recorded on the DVD-RW is performed. The DVD-RW specifications specifies that the embossed area is positioned inside the common detection position and at the time of the reproduction for the DVD-RW it is necessary to obtain the reproduction control information recorded in a certain area inside the embossed area. A record position on the DVD-RW of the reproduction control information is also defined in accordance with the DVD-RW specifications (hereafter, the record position is referred to a target position).
Considering the above-mentioned fact, at the time of starting the reproduction of the information recorded on the DVD-RW, it is required that the start processing is done by emitting the light beam to the common detection position outside the embossed area, thereby obtaining the detection signal, after that, shifting the emitted position with the light beam, namely, a light spot, beyond the embossed area, and emitting the light beam to the target position inside the embossed area to obtain the reproduction control signal.
In this case, if the conventional shifting method is employed when the light spot is shifted, it may be considered to count the number of tracks formed on the DVD-RW which the light spot passed during its shift, and then shift the light spot to the target position while recognizing the position on the DVD-RW of the light spot based on the counted result.
However, if the conventional shifting method is applied to the DVD-RW, the number of tracks, whose width in a radius direction and interval are similar to those of a groove track, formed within the embossed area by using phase pits can not be accurately counted depending on a method of detecting and counting the tracks. As a result, the number of passed tracks is indistinct at the time of the shift of the light spot in the embossed area. This results in a problem that the light spot may not be accurately shifted to the target position beyond the embossed area.
The present invention is proposed in view of the above-mentioned problems. It is therefore an object of the present invention to provide a servo control apparatus and a servo control method which even if a light spot needs to be shifted beyond an embossed area, can shift it to a target position accurately and surely, and an information. reproducing apparatus including the same.
The above object of the present invention can be achieved by a servo control apparatus carrying out a servo control when information is reproduced by using a light beam on an information record medium in accordance with the present invention. The information record medium has a signal change area where a detection signal obtained from the information record medium on the basis of reflection light of the light beam indicates a different characteristics compared with that of the detection signal obtained during the reproduction of the information. The servo control apparatus includes: a detecting device which detects a position of a light spot formed by the light beam except the signal change area on the information record medium; and a shifting device which shifts the light spot beyond the signal change area to a predetermined target position to be radiated with the light beam, which is positioned in another side of the signal change area on the information record medium, on the basis of the detected position.
According to the apparatus, the detecting device detects the position of the light spot formed by the light beam except the signal change area on the information record medium. Then the shifting device shifts the light spot beyond the signal change area to a predetermined target position to be radiated with the light beam on the basis of the detected position. The target position is positioned in another side of the signal change area on the information record medium
Therefore, the light spot is shifted beyond the signal change area where the detection signal indicates a different characteristics compared with that of the detection signal obtained during the reproduction of the information so that the servo control is disturbed. As a result, the light spot can be sent to the target position accurately and surely.
In one aspect of the servo control apparatus of the present invention, a sub-detecting device detects that the light spot is shifted from the detected position to an end of the signal change area. Then the shifting device shifts the light spot from the end to the target position beyond the signal change area after the light spot is shifted to the end.
According to this aspect, after a light spot is shifted to the end, it is shifted to a target position. Therefore, it can be surely shifted beyond a signal change area.
In another aspect of the servo control apparatus of the present invention, the detecting device detects the position as an address information on the information record medium in which the information is recorded.
According to this aspect, even if a position of an information record medium itself is changed, it is possible to surely detect a position of a light spot and send to a target position.
The above object of the present invention can be achieved by a servo control apparatus carrying out a servo control when information is reproduced by using a light beam on an information record medium in accordance with the present invention. The information record medium has a signal change area where a detection signal obtained from the information record medium on the basis of reflection light of the light beam indicates a different characteristics compared with that of the detection signal obtained during the reproduction of the information. The servo control apparatus includes: a detecting device which detects an end of the signal change area; and a shifting device which shifts a radiating position of the light beam beyond the signal change area to a predetermined target position to be radiated with the light beam, which is positioned in opposite side of the signal change area to a side where the end is detected on the information record medium, on the basis of the detected end.
According to the apparatus, the detecting device detects the end of the signal change area. Then the shifting device shifts the. radiating position of the light beam beyond the signal change area to a predetermined target position to be radiated with the light beam on the basis of the detected end. The target position is positioned in opposite side of the signal change area to a side where the end is detected on the information record medium.
Therefore, the light spot is shifted beyond the signal change area where the detection signal indicates a different characteristics compared with that of the detection signal obtained during the reproduction of the information so that the servo control is disturbed. As a result, the light spot can be sent to the target position accurately and surely.
In another aspect of the servo control apparatus of the present invention, the detection signal obtained in the signal change area is an RF signal corresponding to the information, and a level of the RF signal is dropped in the signal change area as compared with that of RF signal obtained during the reproduction of the information.
According to this aspect, even if there is the signal change area in which the level of the RF signal is dropped in the information record medium, the light beam can be surely sent to the target position beyond the signal change area.
In another aspect of the servo control apparatus of the present invention, the shifting device comprises a stepping motor.
According to this aspect, it is possible to send the radiating position of the light beam to the target position while controlling at an accuracy of a step in the stepping motor.
In another aspect of the servo control apparatus of the present invention, the information record medium is DVD-RW, and a phase pit is formed within the signal change area.
According to this aspect, even if there is the signal change area in which the phase pit is formed on DVD-RW, the light beam can be surely sent to the target position beyond it.
The above object of the present invention can be achieved by an information reproducing apparatus in accordance with the present invention. The information reproducing apparatus includes the above-mentioned servo control apparatus and a reproducing device which reproduces the information from the information record medium on the basis of the detection signal.
According to the apparatus, the servo control apparatus carries out the servo control in the above-mentioned manner. Then, reproducing device reproduces the information from the information record medium on the basis of the detection signal.
Therefore, by sending the light beam to the target position accurately and surely, it is possible to surely detect and reproduce an information recorded at the target position and the like.
The above object of the present invention can be achieved by a servo control method of carrying out a servo control when information is reproduced by using a light beam on an information record medium in accordance with the present invention. The information record medium has a signal change area where a detection signal obtained from the information record medium on the basis of reflection light of the light beam indicates a different characteristics compared with that of the detection signal obtained during the reproduction of the information. The information reproducing method includes the process of detecting a position of a light spot formed by the light beam except the signal change area on the information record medium, and the process of shifting the light spot beyond the signal change area to a predetermined target position to be radiated with the light beam, which is positioned in another side of the signal change area on the information record medium, on the basis of the detected position.
According to the method, the position of the light spot formed by the light beam in one side of the signal change area on the information record medium is detected. Then, the light spot is shifted beyond the signal change area to the predetermined target position to be radiated with the light beam on the basis of the detected position. The target position is positioned in another side of the signal change area on the information record medium.
Therefore, since the light spot is shifted beyond the signal change area in which the detection signal indicates the different characteristics compared with that of the detection signal obtained during the reproduction of the information so that a servo control is disturbed, the light spot can be sent to a target position accurately and surely.
The above object of the present invention can be achieved by a servo control method of carrying out a servo control when information is reproduced by using a light beam on an information record medium in accordance with the present invention. The information record medium has a signal change area where a detection signal obtained from the information record medium on the basis of reflection light of the light beam indicates a different characteristics compared with that of the detection signal obtained during the reproduction of the information. The information reproducing method includes the process of detecting an end of the signal change area, and the process of shifting a radiating position of the light beam beyond the signal change area to a predetermined target position to be radiated with the light beam, which is positioned in opposite side of the signal change area to a side where the end is detected on the information record medium, on the basis of the detected end.
According to the method, the end of the signal change area is detected. Then, the light spot is shifted beyond the signal change area to the predetermined target position to be radiated with the light beam on the basis of the detected end the target position is positioned in opposite side of the signal change area to a side where the end is detected on the information record medium.
Therefore, after the end of the signal change area, in which the detection signal indicates the different characteristics compared with that of the detection signal obtained during the reproduction of the information so that a servo control is disturbed, is detected, the radiating position of the light beam is shifted to the target position beyond the signal change area. As a result, the light beam can be sent to the target position accurately and surely